<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
    .box{
        width: 200px;
        height: 200px;
        border:1px solid red;
        display: flex;
        flex-direction: column;
        justify-content: center;
        text-align: center;
        align-items: center;
    }
    span{
        width: 100px;
        height: 100px;
        display: inline-block;
        background-color: aqua;
    }
    </style>
</head>
<body>
    <div class="box">123
        <span></span>
    </div>
</body>
</html>